Methods for producing biodiesel by transesterification of vegetable oils or animal fats are known e.g. from DE 10 2006 044 467 B4.
Furthermore, for example from the specialist article “The Role of Sterol Glucosides on Filter Plugging”, Inmok, Lee et al., Biodiesel Magazine, April 2007, it is known that in the transesterification of natural fats or oils with alkyl alcohol the stearyl glycosides naturally present in the fats or oils largey lose their solubility both in oil or fat and in the fatty acid alkyl ester obtained by transesterification, so that they are precipitated as fine suspended particles and in use of the fatty acid alkyl ester as biodiesel lead to cloggings of the diesel filters and to deposits in the engine.
Methods for removing the stearyl glycosides from the fatty acid alkyl ester obtained by transesterification by means of adsorption are also known.
In WO 2009/132670 a method for purifying biodiesel is presented, in which an adsorbent containing a smectite-silica gel mixed phase is especially used for removing stearyl glycosides. In the examples described in this document, calcium bentonite as comparative material is used as adsorbent. The experiments were carried out in that the adsorbent, at room temperature, was stirred into the fatty acid alkyl ester to be purified and subsequently was filtered off. There was measured a distinctly lower adsorption capacity with respect to stearyl glycosides of the calcium bentonite as compared to a smectite-silica gel mixed phase.
For regenerating the adsorption column, mixtures of alkanes or chlorinated hydrocarbons are proposed in this document, WO 2009/132670, and the use of a mixture of chloroform and methanol in the experiment is described. In particular the chlorinated hydrocarbons and chloroform are substances with a high hazard potential for health and environment.
Therefore, it has been an object to develop a method for producing biodiesel, in which the removal of the sterol glycosides is effected by using inexpensive adsorbents, such as bleaching earths, but which can do without these dangerous auxiliaries for regenerating the adsorbents.